partial Merge bitcoin#8456: [RPC] Simplified bumpfee command.

It includes only this commit for sake of backporting HasWalletSpent

[RPC] bumpfee

This command allows a user to increase the fee on a wallet transaction T, creating a "bumper" transaction B.
T must signal that it is BIP-125 replaceable.
T's change output is decremented to pay the additional fee.  (B will not add inputs to T.)
T cannot have any descendant transactions.
Once B bumps T, neither T nor B's outputs can be spent until either T or (more likely) B is mined.

Includes code by @jonasschnelli and @ryanofsky

Author: mrbandrews

src/wallet/wallet.cpp

@@ -495,6 +495,13 @@ std::set<uint256> CWallet::GetConflicts(const uint256& txid) const
     return result;
 }
 
+bool CWallet::HasWalletSpend(const uint256& txid) const
+{
+    AssertLockHeld(cs_wallet);
+    auto iter = mapTxSpends.lower_bound(COutPoint(txid, 0));
+    return (iter != mapTxSpends.end() && iter->first.hash == txid);
+}
+
 void CWallet::Flush()
 {
     GetDatabase().Flush();

src/wallet/wallet.h

@@ -1190,6 +1190,9 @@ class CWallet final : public WalletStorage, public interfaces::Chain::Notificati
     //! Get wallet transactions that conflict with given transaction (spend same outputs)
     std::set<uint256> GetConflicts(const uint256& txid) const EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
 
+    //! Check if a given transaction has any of its outputs spent by another transaction in the wallet
+    bool HasWalletSpend(const uint256& txid) const;
+
     //! Flush wallet (bitdb flush)
     void Flush();